1. Field of the Invention
The present invention relates to an image processing device, an image processing program and an image combining method, and more particularly to an image processing device, an image processing program and an image combining method for forming a composite image by superimposing an overlay image on a base image.
2. Description of Related Art
In recent years, with respect to image data which is stored to be printed or for other purposes, various kinds of image data compressing methods for reducing the volume of the stored data have been suggested. Also, various kinds of methods for combining two or more images have been suggested.
An example of forming and printing composite images is inset printing, in which changeable overlay images (for example, seat numbers) are superimposed on a fixed base image (for example, a theater ticket), and the formed composite images are succesively printed.
Japanese Patent Laid-Open Publication Nos. 2003-46738 (Reference 1), 6-164950 (Reference 2), 2002-271791 (Reference 3) and 7-336675 (Reference 4) disclose data encoding methods of GBTC type. In these methods, image data is divided into a plurality of blocks, and for each block, a statistical parameter, such as a gray level representing the block, and quantization levels of the respective pixels in the block are encoded to form compressed data with a fixed length.
Reference 4 discloses a method for forming a composite image by superimposing an image B on an image A. In this method, if a block of the image B completely covers a block of the previously written image A, the encoded data of the block of the image A is updated (see paragraph 0007 of Reference 4).
In other words, in the method disclosed by Reference 4, since the image B has priority over the image A, in the region of the image B, the image A is completely deleted. Therefore, if the image A and the image B are of the same size, the base image A will be wholly deleted.
In the case of the above-mentioned inset printing, if the base image and the overlay image are of the same size, or if the overlay image is relatively large, according to the method disclosed by Reference 4, the entire or a large part of the base image A will be deleted.